Owing to generalization of information communication services, advent of a variety of multimedia services, appearance of high quality services, and the like, the demand for communication services are rapidly increased. A research is in progress on a variety of wireless communication techniques in various fields to satisfy such demand.
Multiple input multiple output (MIMO) technique is spotlighted as the technique of high frequency efficiency for enhancing reliability of links and preventing interference between the links. The MIMO technique allows the signals that are independently transmitted through multiple transmit antennas to obtain diversity gain.
A MIMO system using multiple antennas can enhance a transmission rate and reduce probability of packet error by allocating an orthogonal resource to a user to avoid interference among users. The MIMO system can enhance the transmission rate by assigning a single orthogonal resource to a plurality of users. A transmission method of the MIMO system includes a spatial multiplexing method for transmitting user data on each antenna and a method of transmitting data of each user data on each virtual spatial layer through pre-coding.
The MIMO system can be divided into a point-to-point communication system, such as a single user MIMO, and a point-to-multipoint communication system, such as a multiple user MIMO. In the point-to-multipoint communication system, such as a multiple user MIMO, an interference pre-subtraction method performed by a transmitter is recently spotlighted. If it is assumed that a signal u1 is transmitted for a first user and a signal u2 is transmitted for a second user, a transmitter pre-subtracts the signal u1 from the signal u2. At this point, a receiver of the second user can receive only the signal u2 as if there is no interference. According to this technique, the receiver does not need to separately remove interference, and thus complexity of the receiver can be greatly reduced. One of such methods is called as dirty paper coding (DPC). “M. Costa, Writing on Dirty Paper, IEEE Trans. on Inf. Theory, vol. IT-239, No. 3, May 1983” can be referenced for the DPC. In the reference, Costa demonstrates through the DPC that channel capacity under a transmit power constraint is the same as channel capacity when interference does not exist.
However, a method or apparatus for efficiently implementing the DPC in point-to-multipoint communication has not been disclosed. Furthermore, although the MIMO technique can implemented a high transmission rate, examples of utilizing DPC are difficult to find. Accordingly, a technique for enhancing performance of a system by combining MIMO and DPC is required.
Furthermore, a transmission rate is not easy to control when transmitting data if there is a plurality of data streams, due to complexity of a MIMO encoding scheme and the like. In addition, data streams needs to be transmitted only to certain users among a plurality of users. Accordingly, a plurality of data streams needs to be efficiently distributed and transmitted within limited radio resources.